The need for a soft, strong, thermoplastic elastomer for pharmaceutical or medical products continues to exist even though many new materials have been developed. Some materials have some of the desired properties, to some degree. Silicone can be formulated into soft, strong, products but in many applications, silicone products are far too expensive, particularly when large quantities of the products are to be produced. Nothing presently available gives a unique combination of low hardness and useful strength at a resonable cost. Particularly of interest would be products having low hardness and high strength along with some amount of clarity.
Various combinations of synthetic materials have been attempted in order to achieve various end product properties. In U.S. Pat. No. 4,598,123, clear cast acrylic sheets of improved impact strength are prepared by dissolving or dispersing a minor amount of an ABA block copolymer into a methyl methacrylate casting mixture which contains some styrene, followed by polymerization in sheet form via heating with an initiator. The resulting product had improved impact resistance and some formulations remained clear. The hardness, based on the Rockwell R Scale, was at least 77, indicating a very hard product.
Another formulation is described in U.S. Pat. No. 4,440,815. In this patent, 45% to 70% by weight of a polyolefin such as polypropylene is mixed with from 5% to 25% of an ethylene/lower alkyl acrylate copolymer and 10% to 40% of an ethylene butulene block copolymer having terminal styrene blocks. The material is stated to be suitable for sheet extrusion, injection molding or blow molding into flexible, transparent, autoclavable intravenous solution containers which withstand heavy impact during shipment and which also is sufficiently flexible to collapse during drainage of intravenous solutions. The product produced in Example 4 of that patent indicates a hardness on a Shore A Scale of 52, which is still considered to be very hard for many applications.
A strong and soft theromplastic elastomer is still not available for the medical and pharmaceutical industries. Such an elastomer, particularly if it could be produced with some clarity, would form the basis of many practical and useful formulations.